The invention is related to turbines which include turbine blades connected to a rotating shaft of the turbine and nozzles which direct steam or combustion gases to the nozzles.
In a typical turbine used in the power generation industry, fuel is burned in a combustion zone and the hot combustion gases are then directed to the turbine section. In the turbine section, as illustrated in FIG. 1, a plurality of blade assemblies are mounted on a rotating shaft 16. The blade assemblies are attached around the exterior circumference of the rotating shaft 16. Each row of blade assemblies is positioned between an adjacent pair of rows of nozzles or vanes 16, 20. As shown in FIG. 1, a first row of turbine blades 22 is positioned between an adjacent pair of nozzles 18 and 20.
The first row of nozzles 18 directs the hot combustion gases in a desired direction as it impinges upon the turbine blades 22. The passage of the combustion gas over the turbine blades exerts a force on the blades that causes the attached shaft 16 to rotate. FIG. 2 illustrates a typical blade assembly which would be attached to a rotating shaft of the turbine. The blade assembly includes a mounting portion 10 which physically couples the blade assembly to the rotating shaft. A base 45 is attached to the top of the mounting portion 10. A blade 40 extends upward from the top surface of the base 45.
The space located inside the nozzles and blades, close to the center of the turbine, is typically referred to as the wheel space 15. As noted above, hot combustion gases are passing the direction of arrow 38, as shown in FIG. 1. The pressure in the gas flow path across the nozzles in the blades tends to be lower than the pressure in the wheel space 15. As a result, any gas located in the wheel space 15 tends to move outward and into the hot gas path 38.
There are localized variations in ambient pressure in the hot gas flow path. For instance, the pressure at the leading edge of each of the blades 40 tends to be higher than the pressure on either side of the blade 40. In some instances, this can result in the pressure adjacent the leading edge of the turbine blades becoming greater than the pressure in the wheel space 15. When this occurs, hot combustion gases from the gas flow path 38 can penetrate downward into the wheel space 15. This essentially represents a loss of the hot combustion gases into the wheel space, which reduces the overall efficiency of the turbine.
One attempt to prevent the hot combustion gases from penetrating down into the wheel space was to add angel wings 32, 33, 34, 35 to the leading and trailing edges of the base of the blade assemblies. Corresponding projections 36 are formed on the leading and trailing edges of the nozzle assemblies. The angel wings on the blade assemblies and the corresponding projections on the nozzle assemblies help to prevent the hot combustion gases from penetrating down into the wheel space. Nevertheless, there is still a problem with loss of the hot combustion gases, which represents an undesirable inefficiency of the turbine.